1. Field of the Invention
The present invention relates to image projector systems and, more particularly, to an image projector system of the type in which an image formed on a liquid crystal panel is projected by light and displayed on a screen as an enlarged image.
2. Description of the Background Art
As a system for displaying an image on a large screen, an image projector system such as that shown in FIG. 1 is known. The image projector system 1 is installed, for example, on a ceiling 3 of an airplane, and an image projected from the system 1 is displayed on a screen 2, thereby allowing a large number of passengers to view a movie or various kinds of image information.
As shown in FIG. 2, the conventional image projector system 1 includes a light source 11 for emitting parallel rays of light, a liquid crystal panel 12, and a projection lens 14. The liquid crystal panel 12 is composed of a large number of pixels 13 each of which is controlled so as to transmit or intercept light on the basis of image information externally supplied. Thus, an image is formed on the liquid crystal panel 12, and this image is projected on the projection lens 14 by light emitted from the light source 11. The image is enlarged by the projection lens 14 and projected on the screen 2, thereby enabling the enlarged image to be displayed on the screen 2.
As shown in FIG. 1, when the image projector system 1 is to be installed in an airplane, the body of the image projector system 1 is commonly installed on the ceiling 3 so that it will not interfere with the passengers when they are viewing the image displayed on the screen 2. Since the screen 2 is installed to extend vertically from the ceiling 3, the image to be displayed is projected on the screen 2 obliquely downward from the image projector system 1.
Accordingly, the distance between the projection lens 14 and the upper side of the screen 2 is shorter than the distance between the projection lens 14 and the lower side of the screen 2. Consequently, when a square image, for example, is displayed on the screen 2, the image is distorted into the shape of a trapezoid in which the top side is relatively short, while the bottom side is relatively long, as shown in FIG. 3.
To correct such trapezoidal distortion, an image projector system 1 in which the optical axis of the projection lens 14 is displaced from the center of the liquid crystal panel 12, as shown in FIG. 4, has been proposed in Japanese Patent Application No. 04-360122 (1992) by the present applicant. In the proposed image projector system 1, the projection lens 14 is installed so that the optical axis thereof is perpendicular to the screen 2. In this state, the relationship between the liquid crystal panel 12, the projection lens 14 and the screen 2 satisfies the condition of LU/MU=LD/MD; therefore, no trapezoidal distortion occurs. Accordingly, the image is normally displayed on the screen 2.
In this image projector system 1, however, since the optical axis of the projection lens 14 is off the mutual center of the light source 11 and the liquid crystal panel 12, the efficiency of utilization of light emitted from the light source 11 is lowered. Therefore, in order to make the luminance of the image on the screen 2 equal to the normal level it is necessary to increase the brightness of the light source 11, which gives rise to the problem that the power consumption increases. In addition, as will be understood from the figure, the aperture of the projection lens 14 must be increased in order to capture and project as an enlarged image all the rays of light transmitted by the liquid crystal panel 12. The increase in the aperture of the projection lens 14 results in an increase in the overall size of the system and also an increase in the cost.
To avoid such problems, another conventional image projector system 1 is provided with a lens (not shown) for directing the light transmitted by the liquid crystal panel 12 toward the optical axis of the projection lens 14. However, with this arrangement, the number of parts required increases and the cost rises.